GB665532A - Tunable very high frequency circuits - Google Patents

Abstract

665,532. Inductances. POLYDOROFF, W. J. Sept. 24, 1949, No. 24595/49. Class 38 (ii). [Also in Group XL (c)] A tunable very high-frequency circuit comprises a variable inductor having a helical portion surrounding and coaxial with a linear portion, and in series with it, a ferro-magnetic core, movable within the helical portion and provided with a longitudinal slot to accommodate the linear portion, and an adjustable capacitor shunted across the free ends of the helical and linear portions. A coil 3 of conductive strip, Fig. 2, is connected in series with a linear conductor 7, coaxial with the coil. The free ends of coil 3 and conductor 7 are connected in two electrodes of a valve 6, and a capacitor 5, shunting the inductor, is formed by a fixed plate carried by the free end of the coil 3 and a movable plate carried by a screwthread on the end of the linear conductor 7. A core 8, provided with a slot 8a, Fig. 2a, moves into the coil 3 from the end which is joined to the conductor 7. The coil may be a conductive cylinder with a helical slot, Fig. 3 (not shown). Fig. 6 shows an arrangement in which the helical slot does not extend to the ends of the conductive cylinder. In this case the capacitor 5 is formed by a cupped member threaded on conductor 7 and co-operating with the solid end of the coil 3. The position of the linear conductor may be adjusted transversely by a screw mounted in an insulating block at the free end of the coil. The arrangement may be used as the tuned circuit of a V.H.F. oscillator, with the junction of the helical and linear portions connected to earth, and the free ends connected to two electrodes of a valve. The circuit may be coupled to a dipole antenna by a single open turn.